1. Field of the Invention
The present invention relates to an assembling apparatus for assembling a body side of an automotive vehicle and an assembling method thereof which is used at a time of assembling the body side such as assembling various kinds of inner parts to a body side outer part.
More particularly, the present invention relates to a work-piece positioning apparatus and a work-piece positioning method for moving and positioning a work-piece gripped by a robot hand to a predetermined welding position.
Furthermore, the present invention relates to a spot welding method for performing a spot welding on the work-piece which is transferred to a predetermined welding state position by a conveyor and the like, by means of a welding gun.
2. Description of the Related Art
In a body side of the automotive vehicle, there is a structure which is assembled by a body side outer and a various kinds of inner parts. The body side outer comprises a front part constituting a part disposed in front of a vehicle body and a rear fender part constituting a part disposed in the rear of the vehicle body. The front part and the rear fender part are joined by welding. After welding together the front part and the rear fender part to construct the body side outer, the various kinds of inner parts are joined to the body side outer by welding. Then the body side of the automotive vehicle is assembled.
In the above assembling operation, as shown in FIG. 1, there is provided a transfer apparatus 205 for transferring a front part 201 and a rear fender part 203 in a state of laying down, for example, as disclosed in Japanese Patent Application Laid-Open Publication No. 7-96397, and a plurality of welding robots 207 for welding the parts 201 and 203 to each other and welding the inner part to the parts 201 and 203.
The transfer apparatus 205 is provided with two transfer bars 209 extending in the transfer direction and capable of moving in the longitudinal direction, and fingers 211 serving as a work-piece receiver for supporting the parts 201 and 203 and disposed on the transfer bar 209. On a table 213 disposed below the transfer bar 209, there is provided a jig 215 which ascends the parts 201 and 203 so as to be apart from the finger 211 and fixedly holds the parts so as to position them at a time of welding. The jig 215 is provided in such a manner as to vertically movable by a lifter. When the finger 211 holding the parts 201 and 203 moves forward together with motion of the transfer bar 209, the parts 201 and 203 are also transferred forward, in a state that the jig 215 is unclamping the parts 201 and 203.
The assembling operation comprises some stages. In a first stage, the front part 201 and the rear fender part 203 are set on the transfer line and fixed and held by the jig 215 which is in an ascent state, and thereafter, both the parts 201 and 203 are temporarily welded to each other by using the welding robots 207. In a second stage, the connection portions for connecting the parts 201 and 203 to each other and small parts which are already assembled to the parts 201 and 203 are additionally welded. Next, in a third stage, the various kinds of inner parts are set to the parts 201 and 203 and are temporarily welded to each other, and thereafter, in a fourth stage, the parts are additionally welded, whereby the welding of the body side is completed.
Finally, in a fifth stage, the body side which is completely welded is stood up by a stand-up apparatus having an oil hydraulic cylinder for an upright positioning mechanism, and thereafter is hung up by the stand-up apparatus to be transferred to the following stage.
However, in the conventional operation of assembling the body side, there are following problems.
(1) In the welding operation for the additional welding by the plurality of welding robots, the welding robots interfere with each other due to an obstruction of the jig 215, thereby deteriorating the operation efficiency. PA1 (2) Since the work-piece W to be assembled as the front part 201 or the rear fender part 203 is supported by the jig 215 at left and right side bottom portions thereof in a state that the work-piece W is laying down in a horizontal direction with respect to the transfer apparatus, the center portion of the work-piece W is bent due to the gravitational force and is deformed. Then, since the welding operation is performed in the bent state, the assembling accuracy is deteriorated. When the jig for supporting the center portion in order to prevent the center portion from bending, the cost is increased, and the operable area for the welding robot is narrowed. PA1 (3) Since at a time of performing the welding operation and the transfer operation, it is necessary to provide a plurality of special jigs 215 and fingers 211 for fixing and holding the bottom surface of the works as the front parts 201 and the rear fender parts 203 in the laying down state the facility cost is required. Particularly, when a plurality types of automotive vehicle are produced in the same line, it is necessary to provide the jigs and fingers for a wide ranged usage so that the facility cost is extremely high. Further, the stand-up apparatus for standing the work up after welding requires also a high cost.